(a) Field of the Invention
The present invention relates to an adjusting device, and more particularly to an adjusting device for a lower knife of a sewing machine.
(b) Description of the Prior Art
A sewing machine which is commercially available at present is shown in FIG. 1 and comprises an arm 10 disposed on a base 11 and a needle 12 extending downward from a free end portion of the arm 10 for conducting sewing operations. A board 14 is disposed on the base 11 and is located below the needle 12 and has a pawl 15 disposed therein for feeding the cloth to be sewed forward during operations. The sewing machine, for example, an overlock sewing machine for forming a hem or a selvage on the edge portions of a piece of cloth, comprises an upper knife 16 movable downward toward a lower knife 90 in order to scissor and to trim the edge portions of the cloth before sewing operations or before the formation of the hem. As shown in the drawing, the cutting edge of the upper knife 16 is tapered and has a lower edge extending downward beyond the upper edge of the lower knife 90. The upper knife 16 is biased by a spring (not shown) so that the lower edge of the upper knife 16 is biased to contact the lower knife 90 and so that the cloth can be trimmed by the knifes 16 and 90.
A conventional lower knife 90 is shown in FIG. 8 and is fixed to a rod 91 by a screw 92, the rod 91 is slidably received in a support 93 and can be fixed in place by a bolt 94. The width, for example, of the hem or the selvage to be formed on the edge portions of the cloth is varied according to the materials of the cloth and is determined by the distance between the needle 12 and the lower knife 90. The location of the lower knife 90 should be changed and adjusted in accordance with a selected width of the selvage. However, in order to adjust the position of the lower knife 90, an additional tool, such as a wrench, is required to unthread the bolt 94 so that the rod 91 can be moved relative to the support 93, and is required to thread the bolt 94 again so as to fix the rod 91 in place. This is very inconvenient.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional sewing machines.